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(#) Nested scrolling widgets

!!! WARNING: Nested scrolling widgets
   This is a warning.

Id
:   `NestedScrolling`
Summary
:   Nested scrolling widgets
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Resource files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/NestedScrollingWidgetDetector.java)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NestedScrollingWidgetDetectorTest.kt)
Copyright Year
:   2011

A scrolling widget such as a `ScrollView` should not contain any nested
scrolling widgets since this has various usability issues.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
res/layout/scrolling.xml:11:Warning: The vertically scrolling ScrollView
should not contain another vertically scrolling widget (ListView)
[NestedScrolling]
    &lt;ListView
     --------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`res/layout/scrolling.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"
    android:layout_height="match_parent"&gt;

    &lt;LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"&gt;

        &lt;ListView
            android:layout_width="match_parent"
            android:layout_height="match_parent" /&gt;

    &lt;/LinearLayout&gt;

&lt;/ScrollView&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NestedScrollingWidgetDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `NestedScrollingWidgetDetector.testNested`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute `tools:ignore="NestedScrolling"` on
  the problematic XML element (or one of its enclosing elements). You
  may also need to add the following namespace declaration on the root
  element in the XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;ScrollView xmlns:tools="http://schemas.android.com/tools"
      tools:ignore="NestedScrolling" ...&gt;
    ...
  &lt;/ScrollView&gt;
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="NestedScrolling" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'NestedScrolling'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore NestedScrolling ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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